Valves with piezoelectric actuators have been proposed. For example, some designs include an amplified piezoelectric actuator (APA). In APA-based valves, an elastic amplifier element is coupled to the piezoelectric element to mechanically amplify the motion of the piezoelement. A disadvantage of these types of valves is that they are generally limited to a motion range on the order of a few hundred microns, even with the amplifier. Accordingly, adjustment of the amount of flow is limited and therefore the valve is not truly adjustable. As a result, conventional APA valves typically provide only two positions, an open position and a closed position. Other conventional designs include a piezoelectric element for directing flow of a fluid. In such designs, a piezoelectric element is used directly or indirectly to select between two orifices for directing flow of a liquid through a valve body. In operation, when a voltage is applied, the motion provided by piezoelement blocks one port and unblocks another. Although such a valve is controllable, the small range of movement available for piezoelectric elements cannot be used to directly control the amount of fluid flowing through a port. Rather, such a piezoelement controlled valve is generally used in conjunction with a pneumatic actuator to control the amount of fluid flowing through the selected port.
Other conventional piezoelectric valve designs include a valve stem controlled by a unidirectional piezoelectric motor. Such valve designs can regulate directly the flow of various fluids or isolate an evacuated area. Additionally, such valve designs provide a wide range of flow control, high accuracy and resolution, and linear control characteristics. However, the unidirectional nature of the valve limits the functional control characteristics of the valve.